linux-kernel - Re: [PATCH] sched: rt-bandwidth disable fixes

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Date:	Mon, 18 Aug 2008 13:11:16 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Dario Faggioli <raistlin@...ux.it>
Cc:	Stefani Seibold <stefani@...bold.net>,
	linux-kernel@...r.kernel.org, mingo@...hat.com
Subject: Re: [PATCH] sched: rt-bandwidth disable fixes

On Mon, 2008-08-18 at 12:47 +0200, Peter Zijlstra wrote:
> On Mon, 2008-08-18 at 00:15 +0200, Dario Faggioli wrote:
> > On Sat, 2008-08-16 at 23:29 +0200, Stefani Seibold wrote:
> > > After disabling kernel support for "Group CPU scheduler" and applying
> > > 'echo -1 > /proc/sys/kernel/sched_rt_runtime_us' the behaviour is as
> > > expected.
> 
> > > So the problem is located first in the new sched_rt_runtime_us default
> > > value and second in the "Group CPU scheduler".
> > Well, if you have group scheduling configured I think you should do both
> > # echo -1 > /proc/sys/kernel/sched_rt_runtime_us
> > # echo -1 > /dev/cgroup/cpu.rt_runtime_us
> > 
> > if /dev/cgroup is the mount point of the cgroup file system.
> > 
> > In situations like the one you are describing, this worked for me...
> > Hope that it also helps you! :-)
> 
> Ah, right - I knew I was forgetting something..
> 
> (compile tested only)

Right - I knew I was forgetting something... this patch forgets:

  - to allow tasks to groups that have a 0 limit when bandwidth control
is disabled
  - deal with the trouble that gets us in on enabling it again after
that happens.

So, please skip this patch for now..

> ---
> Subject: sched: rt-bandwidth disable fixes
> From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Date: Mon Aug 18 12:39:07 CEST 2008
> 
> Currently there is no way to revert to the classical behaviour if
> RT_GROUP_SCHED is set. Fix this by introducing rt_bandwidth_enabled(),
> which will turn off all the bandwidth accounting if sched_rt_runtime_us
> is set to a negative value.
> 
> Also fix a bug where we would still increase the used time when the limit
> would be set to RUNTIME_INF - causing a long throttle period once it would
> be lowered.
> 
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> ---
>  kernel/sched.c    |    9 ++++++++-
>  kernel/sched_rt.c |   16 +++++++++-------
>  2 files changed, 17 insertions(+), 8 deletions(-)
> 
> Index: linux-2.6/kernel/sched.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched.c
> +++ linux-2.6/kernel/sched.c
> @@ -204,11 +204,13 @@ void init_rt_bandwidth(struct rt_bandwid
>  	rt_b->rt_period_timer.cb_mode = HRTIMER_CB_IRQSAFE_NO_SOFTIRQ;
>  }
>  
> +static inline int rt_bandwidth_enabled(void);
> +
>  static void start_rt_bandwidth(struct rt_bandwidth *rt_b)
>  {
>  	ktime_t now;
>  
> -	if (rt_b->rt_runtime == RUNTIME_INF)
> +	if (rt_bandwidth_enabled() && rt_b->rt_runtime == RUNTIME_INF)
>  		return;
>  
>  	if (hrtimer_active(&rt_b->rt_period_timer))
> @@ -839,6 +841,11 @@ static inline u64 global_rt_runtime(void
>  	return (u64)sysctl_sched_rt_runtime * NSEC_PER_USEC;
>  }
>  
> +static inline int rt_bandwidth_enabled(void)
> +{
> +	return sysctl_sched_rt_runtime >= 0;
> +}
> +
>  #ifndef prepare_arch_switch
>  # define prepare_arch_switch(next)	do { } while (0)
>  #endif
> Index: linux-2.6/kernel/sched_rt.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched_rt.c
> +++ linux-2.6/kernel/sched_rt.c
> @@ -386,7 +386,7 @@ static int do_sched_rt_period_timer(stru
>  	int i, idle = 1;
>  	cpumask_t span;
>  
> -	if (rt_b->rt_runtime == RUNTIME_INF)
> +	if (!rt_bandwidth_enabled() || rt_b->rt_runtime == RUNTIME_INF)
>  		return 1;
>  
>  	span = sched_rt_period_mask();
> @@ -438,9 +438,6 @@ static int sched_rt_runtime_exceeded(str
>  {
>  	u64 runtime = sched_rt_runtime(rt_rq);
>  
> -	if (runtime == RUNTIME_INF)
> -		return 0;
> -
>  	if (rt_rq->rt_throttled)
>  		return rt_rq_throttled(rt_rq);
>  
> @@ -487,13 +484,18 @@ static void update_curr_rt(struct rq *rq
>  	curr->se.exec_start = rq->clock;
>  	cpuacct_charge(curr, delta_exec);
>  
> +	if (!rt_bandwidth_enabled())
> +		return;
> +
>  	for_each_sched_rt_entity(rt_se) {
>  		rt_rq = rt_rq_of_se(rt_se);
>  
>  		spin_lock(&rt_rq->rt_runtime_lock);
> -		rt_rq->rt_time += delta_exec;
> -		if (sched_rt_runtime_exceeded(rt_rq))
> -			resched_task(curr);
> +		if (sched_rt_runtime(rt_rq) != RUNTIME_INF) {
> +			rt_rq->rt_time += delta_exec;
> +			if (sched_rt_runtime_exceeded(rt_rq))
> +				resched_task(curr);
> +		}
>  		spin_unlock(&rt_rq->rt_runtime_lock);
>  	}
>  }
> 
> 
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